How does this song compare life before and after the beginning of the great depression? why do you think the songwriter mentions the soldiers from world war 1?

The reason for mentioning WWI soldiers is during The Depression soldiers from WWI wanted a bonus that was promised them but wanted it early since they along with millions of others were facing desperate times. Not only did the government refuse to pay them but the protest marches by the former soldiers were broken up and the camps they slept in burned. 

The song in general refers to how people were well employed building the country up before the economic collapse ended up literally begging for money or food just to survive.

A. southerners underestimated republicans eagerness to end slavery.